Phase transfer processes between a liquid phase and a gaseous phase and comprising a packed column are quite common in the processing of oilseeds and/or organic compounds like edible oils. In the latter circumstances, phase transfer processes are used to recover the extraction solvent in oilseed extraction plants and also during the refining of edible oils and fats. Edible oils and fats, also referred hereinafter as triglyceride oils, can be of animal origin such as lard or edible tallow, or of vegetable origin such as but not limited to soya bean oil, rapeseed oil, palm oil, and lauric oils like palm kernel oil or coconut oil.
Refining triglyceride oils usually comprises the following steps:                a degumming process to remove phosphorus-containing compounds present in the crude oil,        a neutralisation process to remove free fatty acids,        a bleaching process to remove coloured compounds, and        a deodorisation process to remove malodorous compounds from the bleached oil.        
The number of processing steps involved in the refining of triglyceride oils can often be profitably reduced, for instance by combining the degumming process with the bleaching process in the so-called dry degumming process, and/or by combining the neutralisation process with the deodorisation process in the so-called physical or steam refining process.
The deodorisation process and the steam refining process are vacuum stripping processes. They comprise the steps of degassing the oil to avoid oxygen present in the feedstock from reacting with the triglyceride oil after the oil temperature has been raised, heating the oil to a temperature that can be as high as 270° C. under a vacuum of for example 2-20 mbar, contacting the heated oil with a stripping medium such as steam or nitrogen, and finally cooling the oil. To save energy, various means such as counter-current heat exchangers and thermo-siphons are commonly used.
The deodoriser used in the deodorisation process can be provided with a number of superimposed trays inside the deodoriser shell to ensure intimate contact between the stripping medium and the oil being deodorised or steam refined. The stripping medium may be injected to each tray of the deodoriser through multiple coils and/or gas lift pumps. Another way to establish the required contact between the stripping medium and the oil being deodorised or steam refined is by employing a packed column used in cross-flow mode as described in U.S. Pat. No. 2,991,298 or in counter-current flow as described in U.S. Pat. No. 3,506,696. In the latter, the oil is fed to the top of the packed column and the stripping medium is fed to said packed column from underneath.
The packing material in the packed columns used in the above instances can be Raschig rings as mentioned in U.S. Pat. No. 2,991,298, Pall rings as mentioned in U.S. Pat. No. 3,506,696, a metal cloth as described in German Laid-Open Application 196 05 286 A1, but it can also be a structured packing material as mentioned in U.S. Pat. No. 6,001,220 describing a deodorisation plant for fatty materials. Such structured packing material is for example also described in U.S. Pat. No. 6,713,158, and a method of distributing such a structured packing material inside a packed column in such a way that liquid migration in a transverse, horizontal direction of the column is virtually inhibited has been described in U.S. Pat. No. 5,486,318.
Because the deodoriser operates under vacuum, a pump is used to evacuate the content of the deodoriser and extract both the stripping medium and the organic compounds that entered the stripping gas stream during the phase transfer process between the liquid oil phase and the gaseous stripping medium. To reduce the load on the vacuum pump, said organic compounds are commonly condensed in a so-called scrubber. This condensing step performed in the scrubber can comprise spraying a cooled condensate into the vapour stream by means of one or more sprayers, collecting the condensate stream, cooling it, and recycling the cooled stream to the one or more sprayers. The apparatus used for the condensing step can also comprise a packed column, instead of sprayers, to ensure good contact between the vapour stream and the liquid condensate stream.
Accordingly, a deodoriser shell may contain a number of superimposed trays underneath a scrubber comprising a packed column. This scrubber has to be constructed in such a way that the gas stream that is laden with organic vapours encounters as little resistance as possible when moving through said packed column and that the liquid condensate flowing down said column is kept separate from the triglyceride oil being deodorised or physically refined. To this end, a flat collection sheet provided with slits can be mounted underneath the packed scrubber column, whereby the slits allow the gas stream to move upwards, whereby raised sides around the slits guide the liquid collected on the flat sheet to a condensate collection point, and whereby gutters above the slits prevent liquid from falling down the slits and guide any liquid falling down towards the flat collection sheet.
However, this system of condensate collection has a number of disadvantages. The collection sheet will be relatively cold because the condensate collected onto the sheet has been cooled before being distributed over the scrubber column. Consequently, part of the organic compounds present in the vapour stream being sucked towards the scrubber may well condense against the underside of the collection sheet and the resulting condensate may drop into and contaminate the oil from which it had been removed by vacuum stripping. The system is also difficult to construct and thus expensive to build and operate efficiently.
Therefore there is a need in the art for performing phase transfer processes of organic compounds between a liquid phase and a gaseous phase, e.g. in the vacuum stripping of organic compounds like edible oils and fats, without the complications and/or disadvantages of the prior art. There is also a need in the art for designing an apparatus for performing such phase transfer processes of organic compounds that, due to the concept of construction, can be made, maintained and operated at a minimal cost.